Multidimensional response mechanism of sulfamethazine migration and antibiotic resistome spread in natural riverbed driven by vertical river water level fluctuations

Abstract

In order to elucidate the multidimensional response mechanism for migration of antibiotics and spread of resistome in riverbed driven by river water level fluctuations, dynamic reactors were set up to simulate the variation of sulfamethazine vertical migration, biotransformation and resistance genes expression according to fluctuation direction and magnitude. The upward fluctuation of water level accelerated the migration rate of sulfamethazine with a water-head driven impact index of 2.61 cm/(d•m). However, the downward fluctuation reduced the migration rate from 0.0168 to 0.0103 cm/m on spatial scales and 0.0961 to 0.0241 cm/d at time series, and 27.2% accumulative sulfamethazine was decomposed. The annual accumulation of sulfamethazine in pore water and soil attained 148.24 μg/L and 4.73 μg/g. Water level fluctuations also influenced sulfamethazine degradation rate without changing the metabolic pathways via hydrolysis and oxidative due to the rupture between sulfonamide linked cyclic functional groups with the function of functional genes. However, upward water level decreased 5.26%-8.95% of metabolic functional genes Sad A/B and dmpL and enhanced the resistance genes expression levels of sul1, sul2, and intI1 with 70.03, 59.11, and 177.9 copies/mL, which accelerated the accumulation antibiotics and antibiotics resistance bacteria (ARB). Furthermore, a multidimensional risk assessment framework based on machine learning was developed to quantify resistome spread risk, revealing a 5.69% increase in overall resistome-associated environmental risk, which was predominantly classified as medium to high. This spread trend of antibiotic resistome presented multidimensional response with environmental factors in order of DO> ORP> TOC due to water level fluctuations.